1. Technical Field
The present invention relates to an electro-optical device, such as a liquid crystal device, and an electronic apparatus, such as a liquid crystal projector, including the electro-optical device.
2. Related Art
A liquid crystal device that is an example of an electro-optical device of this type includes a plurality of scanning lines and a plurality of data lines arranged vertically and horizontally in a display region having a plurality of pixels, and a plurality of pixel electrodes at intersections between the scanning lines and the data lines. The liquid crystal device is of an active matrix drive type in which pixel-switching TFTs (Thin Film Transistors) provided to correspond to the pixels are turned on/off, that is, are switched between a selection state and a non-selection state in accordance with scanning signals, and image signals are supplied from the data lines to the pixel electrodes through the pixel-switching TFTs, thereby performing image display.
When the liquid crystal device is driven and a corresponding pixel-switching TFT is switched from the selection state to the non-selection state, parasitic capacitance is generated with a gate insulating film of the pixel-switching TFT as a dielectric film. Parasitic capacitance causes a pushdown phenomenon in which the potential of the pixel electrode is lowered. Due to the pushdown phenomenon, the potential of the pixel electrode, which is set by the image signal to be supplied to the pixel electrode, is lowered, and accordingly display performance of the liquid crystal device is deteriorated. In a liquid crystal device that uses a driving method in which the image signal is supplied to a pixel electrode in forms of an analog signal, luminance of each pixel depends on a voltage to be applied to liquid crystal interposed between the pixel electrode and a counter electrode opposed to the pixel electrode. In such a liquid crystal device, the lowering of the potential of the pixel electrode has a direct effect on the luminance of the pixel, and significantly deteriorates the display performance of the liquid crystal device. The lowering of the potential of the pixel electrode occurs to a greater or lesser extent even if a storage capacitor is connected between the pixel-switching TFT and the pixel electrode in order to maintain the potential of the pixel electrode. JP-A-2002-341313 discloses a technology that suppresses the lowering of the potential of the pixel electrode due to the pushdown phenomenon.
In a liquid crystal device that is an example of an electro-optical device of this type, an inversion driving method, such as dot inversion, line inversion, or frame inversion, is used in order to prevent burning or aging of liquid crystal. In a liquid crystal device that uses an inversion driving method, the potential of the pixel electrode in each pixel has one of a positive polarity and a negative polarity in a positive write period or a negative write period according to the potential of the counter electrode opposed to the pixel electrode. The potential of the image signal to be written to the pixel electrode or the potential of the counter electrode is adjusted such that the voltage to be applied to liquid crystal in each period becomes constant.
In the technology disclosed in JP-A-2002-341313, there is a problem in that the configuration of a pixel circuit provided in each pixel for driving liquid crystal is complicated. In addition, when the pixel is reduced in size to allow high-definition images to be displayed in the display region, it is difficult to ensure a space in the pixels in which to dispose the TFTs and wiring lines connecting the TFTS. If the TFTs and the wiring lines can be formed in the pixels, the potential of the pixel electrode may be lowered due to parasitic capacitance between the element, such as the TFT, and the wiring line, and the image signal may be insufficiently written to the pixel electrode. In addition, in the electro-optical device of this type, a precharge operation to precharge a data line may be performed after a first frame period of adjacent frame periods such that the potential of the image signal to be supplied to the data line is not changed during a subsequent frame period. According to the technology disclosed in JP-A-2002-341313, in order to suppress lowering of the potential of the pixel electrode, a predetermined period is needed after the image signal is written to the pixel electrode. For this reason, it becomes technically difficult to ensure a period in which the precharge operation is to be executed.
In the liquid crystal device that uses an inversion driving method, an image signal whose potential is adjusted by means of an external circuit, such as an image signal supply circuit, is supplied to a data line. For this reason, adjustment of the potential of the image signal becomes complicated, and the configuration of the external circuit, which executes such adjustment, also becomes complicated. In addition, it is necessary to adjust the potential of a positive-polarity image signal or a negative-polarity image signal to be higher than a target potential in advance. Accordingly, in driving the pixel-switching TFT for supplying the image signal to the pixel electrode, the voltage of the scanning line to be applied from the scanning line to the TFT needs to be increased, and voltage resistance of the scanning lines needs to be increased.